A conventional electronic control unit controls a control target by a microcomputer, which executes a variety of functions. In an electronic control unit used for controlling an automotive vehicle, for example, a core is configured to be operable with a voltage lower than that of an input/output circuit so that a microcomputer operates at high speeds to meet high functionality.
JP 2006-293492 A, for example, discloses an electronic control unit having a microcomputer, in which a core and an input/output circuit are provided and the core is operable with an operating voltage lower than that of the input/output circuit, a power supply circuit, which supplies operating voltages to the core and the input/output circuit by stepping down an external power supply voltage supplied from an external side, and a peripheral circuit part.
To meet high functionality of the microcomputer, an operating frequency of a digital circuit such as the core is increased and a circuit size of the digital circuit is increased. Thus the microcomputer consumes more current. With increased current consumption, the electronic control unit consumes more power and generates more heat. The core of the microcomputer consumes more current, which is supplied from a power supply circuit part, than other circuits.